Plasma can be used in coating, etching, or ashing processes. A very common plasma process is so-called sputtering, in which atoms are removed from a target by means of accelerated ions from the plasma. The atoms are then deposited on a substrate. Reactive gases are often added in the sputtering process, in order to deposit compounds such as, e.g. Al2O3, on the substrate. This type of sputtering is called reactive sputtering. In reactive sputtering insulating layers can also be formed on the target. Insulating layers of this kind can be charged by the ions that are accelerated onto the target. If the field strength of an insulating layer that has been charged in this manner exceeds the breakdown field strength, arc discharges (also called arcs) can be formed. Arc discharges can be short-lived and self-extinguishing (so-called short or micro arcs), or long-lived and highly energetic (so-called hard arcs). Short arcs for the most part only cause minor damage and can be allowed to occur for many processes, e.g. glass coating. Hard arcs can lead to the destruction of the target and to imperfections on the substrate. Appropriate countermeasures are therefore used to extinguish hard arcs.
To initiate the above cited measures, devices for the detection of arc discharges (arc detection) and also for the suppression or extinction of the arc discharges (arc suppression) are in many cases an integral part of a plasma power supply.
A reliable detection of arc discharges or arcs is important. At the output of the plasma power supply, an arc discharge can be detected by detecting a dip or a decrease in voltage, or an increase in current. In other words: by monitoring at least one appropriate parameter, e.g., an electrical parameter of the plasma process, arc discharge detection can be performed.
As above indicated, in the plasma process not only long-lived arc discharges (hard arcs) can occur, which under certain circumstances lead to a complete destruction of the substrate or the target, but also short or micro arcs (in the following summarized as short arcs) can occur. Short arcs are regularly less pronounced and self-extinguishing. However, it is also known that a short arc can grow into a hard arc if no appropriate countermeasure is executed.